First of all, I really agree with all the people who said that you should get a major in that field which most interests you (and where you have a chance at getting good grades as well!).
Having said that, one of my majors was in philosophy, and I think that I was very fortunate to major in that field. First of all, it really helped me a lot, when it came to the LSAT. In order to get a degree in philosophy (at least at my university), you are required to take an elementary course in logic. Logic is hard, but if you learn it and become good at it, it will really help you on the LSAT. For me logic was very hard, but I studied a lot and got a 4.0 in the class. Then I took an advanced logic course and got a 4.0 in that as well. When it came time to look over the LSAT, everything was familiar territory. In fact, when I was taking an LSAT prep class, I found myself often giving suggestions to my instructor on what logical rules to use or how to diagram the problem, based on what I learned in my philosophy logic classes.
Also in philosophy you do a lot of analytical reasoning - analysis, critique and formulation of arguements - this is what philosophy is all about. This is what the largest part of LSAT is also about: you're given an arguement and you have to analyze it - strengthen, weaken, adjust it, etc. To someone who studied philosophy this sort of thing is nothing new: you've done this kind of analysis with very complex arguements every day as an undergrad.
Further, from what I understand, once you are in law school you will also have to analyze, critique, and formulate arguements, especially on exams. And (from what I understand, I am not in law school yet) a lot of the work in law school will involve reading monotonous dry and complicated reading material, understanding it all, and being able to summerize and analyze it. Well, if you've ever read, understood and analyzed Kant or Hegel, I think that you will be prepared for any reading that law school might offer.
Finally, in philosophy classes you write, write, write like crazy. And your writing is about very complex ideas and arguements that you have to analyze and comment on.
So the point is that majoring in philosphy might be extremely helpful for a future lawer. But you do need to like philosophy to choose it as your major and be able to do well in it. Be warned that it is a tough major.